High-pressure Raman study of liquid and crystalline C2H2

Raman spectra were measured for liquid (0–0.7 GPa), crystalline cubic (0.7–0.9 GPa), and orthorhombic (0.9–3.5 GPa) phases in C2H2 at room temperature. For the orthorhombic phase, the high-pressure behavior of the librational and internal vibrations was obtained in a wide pressure range. The frequencies of all the librational modes increased monotonically with pressure, while those of the internal modes showed a variety of frequency shifts depending on vibrational mode. These high-pressure data will be of great use for the construction of theoretical models for the intermolecular interactions in crystalline C2H2.